Sewashi Nobi, the great-great-grandson of Nobita Nobi and Shizuka Minamoto, hails from the 22nd century. Determined to reverse a debt-ridden future caused by Nobita’s failures, he journeys to the past to alter his ancestor’s trajectory. His solution is deploying the robotic cat Doraemon, tasked with staying beside Nobita until his life improves through an embedded “accomplishment program.” Visually mirroring Nobita, Sewashi typically forgoes glasses, sporting fair skin, black hair, and large eyes. His design shifts across adaptations: *Stand by Me Doraemon* features him with ginger hair, contrasting earlier black-haired iterations. Outfits evolve from red-and-white jumpsuits in the 1973 anime to sleeker teal-and-white ensembles in modern portrayals. Academically challenged like Nobita, Sewashi compensates with heightened athleticism and a sense of duty. Shared familial quirks emerge in his dental phobia, echoing Nobita’s anxieties. Though serious, he displays empathy, vigilantly tracking Nobita and Doraemon’s journey and mediating their disputes with genuine care. A defining moment involves his robotic mouse, which gnawed Doraemon’s ears, triggering the robot’s rodent phobia and emotional collapse. This mishap bleached Doraemon’s yellow coat to blue, cementing Sewashi’s unintended impact on his companion’s identity. Sewashi’s lineage includes rarely depicted parents—his mother mirrors Nobita’s mother in futuristic attire—and great-grandfather Nobisuke, Nobita and Shizuka’s son. His mission to dismantle the family’s cycle of hardship intertwines with fan speculation that he manipulated historical records, creating a causal loop to secure his existence. In *Stand by Me Doraemon*, Sewashi’s orchestration kickstarts Nobita’s transformation. Blending futuristic tech with calculated strategy, he balances pragmatic problem-solving with a quiet, familial devotion, ensuring his interventions carry both logical purpose and emotional depth.